1. Field of the Invention
This invention is in the field of apparatus and methods for manufacturing dental floss holders with high volume injection molding machines which draw one or more continuous strands of dental floss from a supply to and through the mold so that the floss is molded in situ into the dental floss holders which are ejected while still attached to the floss extending both upstream and downstream of the mold. Typically, a multi-cavity mold is used with each strand of floss in the mold spanning a plurality of cavities. This invention further concerns improved efficiency in processing the molded flossers, securing the floss therein and packaging same.
2. Relevant Prior Art
3. Background
Disposable dental floss holders, also called xe2x80x9cflossersxe2x80x9d, have become popular alternatives to using traditional long strands of dental floss wrapped about the user""s fingers. These flossers are now produced in great numbers; however, because each of these devices is quite small and is discarded usually after one or a few uses, it can command only a small sale price. Consequently, a manufacturer must produce huge volumes in the millions in order to be economically profitable. Under these circumstances improved efficiency of manufacture is a most significant aspect for economic viability.
In this high volume manufacture there are many problems including properly positioning the floss in the mold, securing the floss in the holders, minimizing breakage of the continuous strand(s) of floss extending from the floss supply to the point of severing molded flossers from the supply floss, selecting suitable plastic for the handle for the floss with regard to molding temperatures, strength and fraying, and post-molding operations of breaking the holders from the central runner, separating the flossers from each other, securing the floss ends in the handles and finally packaging the holders with efficient mass production techniques.
The present invention concerns a number of problem areas in the manufacturing and packaging process. The first is minimizing breakage of the floss supply lines during molding while maintaining proper predetermined tension in the floss so that the floss in each finished flosser will be relatively straight and taut.
In known high volume injection molding machines for producing dental floss holders, an objective is to maintain the floss in tension while it is drawn into the mold, during molding, and subsequently as quickly as possible to move the ejected aggregate of molded flossers (xe2x80x9cshotxe2x80x9d) out of the mold and to move the next segment of floss into the mold. Also, the shot transported downstream must be severed from the successively molded shots, all the while trying to maintain proper tension in the floss which traverses the mold.
In the above described procedure there are persistent serious problems. When the floss is not properly tensioned in the mold the resulting flossers may have sloppy slack floss, or worse, the floss may be positioned incorrectly in the mold and become damaged. If the floss breaks anywhere between the supply at the upstream end and the severing point at the downstream end, the entire machinery has to be stopped, cleaned up, and new floss fed through the stages and tension re-established.
Such xe2x80x9cdown timexe2x80x9d, if frequent, obviously will greatly diminish efficiency and possibly render the entire process unprofitable. For injection cycles as fast as four to six per minute, for example, breakage of the floss or non-constant tension is recognized as a major problem. The present invention provides a novel apparatus and technique for overcoming this problem.
After the injection molded xe2x80x9cshotsxe2x80x9d or racks of, for example, twenty flossers attached to a central runner are produced, the high efficiency mass production must be maintained during the stages of severing the flossers from the central plastic runner and from each other and securing the floss ends in the holder. The present invention provides new apparatus and techniques for improving this efficiency also.
The new invention is an apparatus ancillary to an injection molding machine, operable with a supply of one or more a continuous strands of dental floss, a supply of injection-moldable plastic, and a multi-cavity mold having mating parts moveable between open and closed positions, with said dental floss extending from said supply between the faces of and through and out of said mold. The molding machine in operation produces a shot of a plurality of dental floss holders molded in situ onto said floss every injection cycle, where every two adjacent shots comprises a set with one of said set being the downstream shot and the other the upstream shot until the upstream shot becomes the downstream shot of the next adjacent shot. This molding machine apparatus further includes (a) first tension means constantly applying a force to said floss upstream of said mold and in the upstream direction, (b) take-off means downstream of said mold engaged to said floss and maintaining tension in the downstream direction by intermittently pulling said floss in said downstream direction, after each injection and ejection phase and holding said floss from moving without pulling in any direction during said injection and ejection stage, and (c) severing means for severing the downstream shot from the upstream shot of each of said sets received by said take-off means while said upstream shot remains engaged to said take-off means and maintains said tension in said floss downstream of said mold.
The second principal phase of this high speedxe2x80x94high volume production process invention concerns taking the molded shots as seen in FIG. 9, each shot containing a plurality of dental floss holders still joined to a central runner, feeder runner and gate and joined to each other via the continuous strand of floss, and proceeding with the steps of separating the individual flossers from the central runner and from each other, securing the floss ends to the holder simultaneously with severing the floss joining adjacent flossers, and finally packaging the flossers either individually or in groups.